Istio is an open-source service mesh that helps manage network architecture without altering application code. It was released in 2017 as a joint project from Google, IBM, and Lyft. Companies like Namely and Trulia use Istio to run their service-oriented architectures. Monitoring the health of your Istio mesh is crucial for maintaining system availability. Key metrics include request counts, request durations, response sizes, xDS client connections, configuration validation results, certificates issued, and dispatches to adapters.